Friday, June 5, 2015

Adjusting level for ABX

My QSC ABX box does have a built-in potentiometer system, though I'm not sure I want to use it for a whole host of audio perfectionist reasons.

Instead, I want to use a small passive attenuator box right before the power amp. This will allow the high impedance output of the attenuator to have as short a cable as possible, perhaps 1f or 0.5M. That's important because with a given amount of source resistance added by the attenuator, an RC network is created, and the longer the cable the more the C and the lower the frequency at which rolloff or phase shift of a particular magnitude appears.

I also want the passive attenuator impedance to be as low as possible. 5k sounds good. It shouldn't be too low, such as 1k or lower, because that often causes more distortion in the source that feeds the attenuator.

The potentiometer should NOT be stepped as it will be necessary to adjust to 0.05dB or better. Fake steps might be OK but I'd rather avoid them. Wirewound may add inductance (but might actually be OK). Two mono pots and not stereo (though two stereo pots would also work).